1. Field of the Invention
This invention relates to a new mixed metal oxide material, in an extruded or spherical form, and process for making said material. More specifically, the invention relates to flash activated hydrotalcite for use as an improved adsorbent, viscosity enhancer, catalyst and/or catalyst support. The invention further relates to an improved process of manufacturing flash activated hydrotalcite powders and formed shapes, the latter having excellent crush load strengths.
2. Technology Review
Hydrotalcite exists in both a natural and synthetic form. Naturally occurring deposits have been found in Snarum, Norway and in the Ural Mountains. Typical occurrences are in the form of serpentines, talc schists, or where hydrotalcite forms the pseudomorph of a spinel. Like most ores, natural hydrotalcite is virtually impossible to find in a pure state. Such deposits often contain one or more other minerals including penninite and muscovite.
Several processs are known for making synthetic hydrotalcite in such product forms as a fine powder, -20 mesh granules or as 1/8-inch diameter extrudates. One representative process is described in U.S. Pat. No. 3,539,306. There, an aluminum hydroxide, aluminum-amino acid salt, aluminum alcoholate, water soluble aluminate, aluminum nitrate and/or aluminum sulfate are mixed with a magnesium component selected from magnesium oxide, magnesium hydroxide or water-soluble magnesium salt and a carbonate ion-containing compound in an aqueous medium maintained at a pH of 8 or more. The resulting product may be used as a stomach antacid. In this typical neutralization process, a fairly pure, finely sized hydrotalcite particle is formed. A serious disadvantage of this process, however, is formation of a sodium salt by-product. Said salt neutralization process could also produce a brucite-like structure with undesired anions (e.g. sulfate) or cations (Na.sup.+).
In Misra Reissue U.S. Pat. No. 34,164, the disclosure of which is fully incorporated by reference, yet another means for synthesizing hydrotalcite is taught. That process comprises heating magnesium carbonate and/or magnesium hydroxide to form activated magnesia, then combining the activated magnesia with an aqueous solution of aluminate, carbonate and hydroxyl ions.
Other known processs for synthesizing hydrotalcite include: adding dry ice or ammonium carbonate to the thermal decomposition product from a magnesium nitrate-aluminum nitrate mixture, after which an intermediate product is subjected to temperatures below about 325.degree. F. and pressures of 2,000 to 20,000 psi. Yet another process, from "Properties of a Synthetic Magnesium-Aluminum Carbonate Hydroxide and its Relationship to Magnesium-Aluminum Double Hydroxide Manasseite, and Hydrotalcite", The American Mineralogist, Vol. 52, pp. 1036-1047 (1967), produces hydrotalcite-like materials by titrating a solution of MgCl.sub.2 and AlCl.sub.3 with NaOH in a carbon dioxide-free system. This suspension is dialyzed for 30 days at 60.degree. C. to form a hydrated Mg--Al carbonate hydroxide having the properties of both manasseite and hydrotalcite.
It is generally known to activate hydrotalcite materials by heating them between about 400-600.degree. C. (752-1112.degree. F.), and preferably at around 500.degree. C. (932.degree. F.), for about 15-60 minutes to drive off carbon dioxide and water from hydrotalcite's basic structure and make it more adsorptive. It is also known to process certain hydrotalcites to generate: needle-like structures, as per Miyata et al U.S. Pat. No. 4,351,814; sheet-like forms, as per Schutz et al U.S. Pat. No. 5,399,329; or spheroidal shapes, as per Cox et al U.S. Pat. No. 5,437,720.
It is a principal objective of this invention to provide means for enhancing the adsorption performance of hydrotalcite powders, said powders having an average particle diameter between about 1 and 100 microns. It is another main objective to provide a hydrotalcite, or hydrotalcite like material, in a more easily useable, transportable product form, such as an extrudate. It is yet another principal objective of this invention to provide an extruded, synthetic hydrotalcite which can withstand 7 lbs. or greater crush loads upon activation. Still another main objective is to provide a process for making commercial quantities of a flash activated (or flash calcined) hydrotalcite.